All bees have to collect nectar and pollen for food. Some bees will collect pollen from almost any flower, while others will only collect pollen from certain plants.
If the flower supply dwindles, most likely due to garbage and pollution, the bees will have a smaller amount of resources. Some bees will barely be affected, while others will lose their source of food almost entirely.
The bees that collect pollen from any flower are the most fit. This is because they are able to find a stable food sources almost anywhere, which would help them survive. Meanwhile, if the other type does not find the type of flower it needs, it will die.
After a while, the bees will adapt to their surroundings. When that happens, there will most likely be more bees that collect anywhere than bees that don't.